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SpaceWire Protocol ID

SpaceWire Protocol ID. Steve Parkes Space Technology Centre University of Dundee Scotland, UK. Aim. The protocol identification scheme aims to allow different protocols to operate concurrently over a SpaceWire network without them interfering with each other

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SpaceWire Protocol ID

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  1. SpaceWire Protocol ID Steve Parkes Space Technology Centre University of Dundee Scotland, UK

  2. Aim • The protocol identification scheme aims to • allow different protocols to operate concurrently over a SpaceWire network • without them interfering with each other • To achieve this an identifier is given to each protocol • Units receiving packets process and respond to them • according to the protocol specified by the protocol identifier on the packet.

  3. Logical Address Protocol ID Logical Address with Protocol ID Path Address Logical Address Protocol ID Path Address with Protocol ID Logical Address • Logical Address always used • After path address removed logical address is present • Check that packet is intended for the node it arrived at • Use 254 if node does not have a logical address

  4. Rest of Packet Rest of Packet EOP EOP Logical Address Protocol ID Logical Address with Protocol ID Path Address Logical Address Protocol ID Path Address with Protocol ID Path Address Path Address Logical Address Protocol ID Rest of Packet EOP SpaceWire Protocol Identifier

  5. Protocol Identifier • Protocol identifier (PID) • single byte • immediately following logical address • PID value of zero reserved for protocol ID extension • PID value of 255 is reserved

  6. Protocol Identifier • PIDs in range 1 to 239 assigned by the SpaceWire working group • PIDs 1 upwards for recommended protocols • PIDs 239 downwards for supported legacy protocols • PIDs 1-239 guaranteed not to clash • i.e. each supported protocol has a unique PID

  7. Protocol Identifier • PIDs in the range 240 to 254 • available for experimental use • might clash with protocols being developed by other users • Concurrent operation of different protocols only assured for protocols in the range 1 to 239 • Proven protocols may be recommended for adoption by the SpaceWire working group • Once adopted • given unique protocol identifier in the range 1 to 239 • added to SpaceWire standard

  8. Ignoring unknown protocols • If packet arrives at destination with PID that is not supported (unknown) by that destination • Destination shall ignore the packet and delete it. • Count of the number of packets with unknown PIDs should be kept and made available by the destination.

  9. Extended Protocol Identifier Logical Address 0 Extn PID Extn PID • PID with value zero (00h) used to extend number of available PIDs • Two more bytes follow reserved zero PID • Forming a 16-bit extended protocol identifier • Allows up to 65535 protocols to be carried over a SpaceWire network • Unlikely that extended PID will be used Logical Address with Extended Protocol ID Extn PID Path Address Logical Address 0 Extn PID Path Address with Extended Protocol ID

  10. Extended Protocol Identifier • Implementation of the extended protocol identifier NOT mandatory • If extended protocol identifier not implement • then reception of a PID of value zero shall be ignored • destination should record count of the number of packets it received with an extended PID • Extended PID with value 000000h is reserved and shall be ignored when received.

  11. Extended Protocol Identifier • Extended PIDs with values in range 000001h - 0000FFh • represent same protocols as non-extended PIDs • with values 01h to 0FFh respectively • e.g. protocol 02h is the same as protocol 000002h. • Extended protocols 000001h-0000FFh are reserved • one byte IDs are used for these protocols

  12. Existing Protocols • Recommended • 1: Remote Memory Access Protocol (RMAP) • 2: SpaceWire working group working on reliable transport protocol • Legacy • 239: STUP for SMCS-332 ASIC configuration • 238: Proposal for RDDP

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